I just beat it on Perfect... the first time I saw the ship I started shooting away at it with the cmp, while opening and closing the door a few times so it wouldn't damage me much. It's better to destroy it early on and not have to deal with it on the next couple floors. Granted I was SLIGHTLY short on ammo later on but I used the rocket to kill one of the guards in the night vision room and finished off fine. I beat it on the first try. Also to avoid damage to Dr. Caroll, I like to close the elevator doors on him every time I go up a level to fight the enemies before he gets there.